1. Field of the Invention
This invention relates to safety equipment for floating roof tanks for hydrocarbons, and more particularly to a control system and valve responsive to the presence of water and pressure within the system to prevent discharge of hydrocarbons through the water drainage outlet.
2. Brief Description of the Prior Art
Open top floating roof tanks are used to store highly flammable liquids, e.g. hydrocarbons, at atmospheric pressure. They are used for storing such materials as gasoline, crude oil, diesel fuel, and various end cuts of the refining process. Each of these tanks are equipped with a roof drain system permitting the flow of rain water from the roof through a flexible connection to a drain outlet near the base of the tank. The drain outlet is connected to a normally closed gate valve. The normally closed valve is to insure that valuable and hazardous hydrocarbon product is not lost at the drain due to a malfunction or leakage in the flexible drain line. As a result, men must be sent to the tank location during a rain to open the valve. Failure to open the valve can, and often does, cause the roof to become so heavy that it will collapse, creating a safety and operations problem. The tank must be taken out of use, drained of all product, cleaned, and repaired all at great expense.
Lerner et al U.S. Pat. No. 3,564,527 discloses an alarm scheme for waste fluid drains comprising a continuously filled sampling conduit which samples the fluid flowing in a drain pipe. The electrical conductivity of the fluid is continuously monitored and on a selected change in conductivity, an alarm device is energized to provide an alarm indication.
Tolin U.S. Pat. No. 2,924,756 discloses an indicating and control probe which will detect materials in terms of their dielectric properties. The detecting circuit comprises a single vacuum tube oscillator having a control device in the plate circuit. Continuous oscillations result in sufficient current flowing through the plate circuit to energize an indicating or control device.
Jarzembski U.S. Pat. No. 2,932,315 discloses a fluid level control system having a transistorized circuit which uses the electrical power supplied by a battery. An electrical capacitor, formed by an electrode and the wall of the container has its value of capacitance determined by the physical proximity of the fluid to a probe electrode. The dielectric constant of the fluid, as the level of the fluid rises to the probe will change the output. The probe capacitance is sensed by the circuit and translated into an electrical current. The result is a positioning of a valve in accordance with the physical distance between the probe and the fluid level in order to maintain that distance at a predetermined value.
Jennings U.S. Pat. No. 3,074,587 discloses an automatic drain for a floating roof tank in which a valve can be maintained in a closed position when there is insufficient water in the drain hose to require immediate draining. The valve will open when water in the hose exceeds a level whereby its static pressure is greater than the static pressure of the liquid in the tank.
Seney U.S. Pat. No. 2,861,159 discloses the determination or control of liquid level by the use of a temperature sensitive probe.
The prior art in general does not disclose a valve and system which shuts off the outlet water drain from a floating roof tank in the absence of water or the presence of hydrocarbons.